The use of inkjet printers for printing information on recording media is well established. Example printers employed for this purpose include continuous printing systems which emit a continuous stream of drops from which specific drops are selected for printing in accordance with print data. Other printers include drop-on-demand printing systems that selectively form and emit printing drops only when specifically required by print data information.
Printing systems that combine aspects of drop-on-demand printing and continuous printing are also known. In these types of printing systems, liquid is continuous circulated through the printing systems but only printing drops are emitted from the printing system when specifically required by print data information. These systems, often referred to as flow through liquid drop dispensers or continuous on demand printing systems, provide increased drop ejection frequency when compared to drop-on-demand printing systems without the complexity of continuous printing systems.
These printing systems include a liquid supply system and a printhead(s) that includes a plurality of nozzles fed by the liquid supply system. Particulate contamination in the liquid, for example, ink ejected from each printing system can adversely affect quality and performance because, for example, the printheads have small diameter nozzles. As such, these types of printing systems typically include one or more filters positioned at various locations in the liquid path to reduce problems associated with particulate contamination.
If, for example, contaminants of diameter D or larger can clog a nozzle or cause the jet emitted from a nozzle to be misdirected, the filter that removes these contaminants should have pores with diameters less than D. As ink passes through the pores of a filter the pressure drop across the filter depends on the diameter of the pores. It is therefore desirable for filters to have pores as large as possible while still filtering out the problem causing contaminants. It is also desirable for the filter to have as many pores as possible, to reduce the pressure drop across the filter.
Many different techniques and combinations of materials have been used for making filters with sufficiently small diameter holes as to capture particulate contamination as small as 4 microns. Punching, laser drilling, molding, and machining are known techniques, however, electroforming is generally considered an effective technique for making articles, such as filters, requiring fine geometric features. One reason for this is because electroformed filters have been found to shed less particulate matter when compared to filters made using the other techniques described above.
The electroforming process, also called an electroplating process, uses an electric current to transfer metal ions from a source metal (for example, nickel) to a conductive object. The source metal and the conductive object are immersed in an electrolyte solution that permits current flow from the source metal to the conductive object. As the current flows, metal ions from the source metal are deposited onto the conductive object to form a metal layer. The deposition rate of the source metal is directly related to the current, with a higher current yielding a higher deposition rate.
In order to form geometric features, such as filter pores, in the plated metal layer, portions of the conductive object are masked by a non-conductive material to prevent metal from being plated onto these regions. When making orifices or filter pores, it is common to plate a metal layer on the conductive object that is sufficiently thick that the plated metal layer overplates a portion of the non-conductive material. As a result, the size of the pore or opening through the metal layer depends on the thickness of the plated metal layer. The thickness of the plated metal layer depends in part on the current density. The current density, which is the current across the surface area of the article being formed, can vary, especially in areas with geometric features. The current density of the ends of the article can differ from the current density in the middle of the part. This can produce electroforming filters with an unacceptably large variation in filter pore diameters.
Therefore, there is an ongoing need for an electroformed filter having a uniform pore diameter that is suitable for use in any of the printing systems described above.